Platen presses perform foil stamping, embossing, or die cutting by compressing a target material between two platens. The target material is placed between the platens while they are separated. Then, a driving force is applied to at least one of the platens to force the platens together. Most implementations of platen presses require that the force between the contacted platens be relatively great. Pressure approaching 2000 pounds per square inch of image is often applied when foil stamping.
To provide such compression forces repeatedly and quickly, a driving mechanism, which is often a crank, is used to drive an arm that moves one of the platens back and forth due to the movement of the driving mechanism. The faster the driving mechanism moves, the greater the frequency of the compressions. A loading mechanism is usually employed to remove the previously stamped material from between the platens and then place new target material therebetween during each compression cycle while the platens are separated.
A glider is typically provided in the arm so that the movable platen and the arm are not rigidly connected. The glider is able to slide along the arm as needed during the impression cycle. In use, the driving mechanism causes the arm to move the platen. In platen presses that use a crank as a driving mechanism, when the crank is at a 0° or initial position, the arm holds the platens in an open position. As the crank rotates toward a 180° position or half a revolution, it pulls the platens together and creates pressure between them.
Springs are used with the glider to provide a longer dwell by allowing the platens to establish contact sooner. One end of the springs is connected to the arm and the other end connects to the glider. When the platens first come into contact, the glider is forced to slide in the direction opposing the biasing force provided by the springs due to the continued movement of the connecting arm. Until rotation of the crank approaches 180° and the arm reaches its maximum distance of travel, the compression force is provided primarily by the springs. This force is only about 1000 pounds which produces pressure well short of the 1 ton per square inch of image pressure that is often necessary.
As the crank continues to turn toward the 180° position, the springs compress and the force remains in the 1000 pound range. Finally, the crank reaches a 180° position or a half revolution and the compression force approaches the tensile strength of the arm connected to the crank due to the springs becoming fully compressed. This force approaches 45 tons for medium sized platen presses. However, the 45 tons of force is only an impulse and is not sustained. As soon as the force has peaked, the crank continues to turn, and the compression force falls back to the compression force provided by the springs until the platens separate.
Platen presses that employ springs to extend the dwell suffer from a lack of flexibility. To alter the impression force so that the springs do not contribute to extend the dwell, the springs must either be removed (and the platen's position adjusted) and replaced with spacer bushings that lock the glider in place or the springs must be locked in place. If the contribution by the springs needs to be altered but not entirely eliminated, the springs must be replaced with springs of a different force.
Furthermore, if a rigid non-extended dwell system is desired and the springs are not removed, the springs must be locked in their extended position by a mechanical blocking device such as a spacer bushing that fits between the springs and locks the glider in place. Inserting the spacer bushing effectively blocks out the springs, and this block out requires that the platen's position be adjusted so the platens do not contact as soon. The platens then must contact closer to the 180° position of the crank because the distance from the glider to the end of the rigid arm remains constant throughout the dwell.
In addition to using a spacer to effectively eliminate the springs' contribution, it is sometimes desirable to alter the duration of the extended dwell without eliminating the dwell extension altogether. Such a configuration requires various size spacer bushings be inserted depending upon the desired duration. The platens must then be repositioned so they contact at the proper time in the crank's cycle.
If an extended dwell is desired and the press is in the non-extended dwell rigid mode where the springs are blocked out, the mechanical blocking device must be removed to free the glider. Because the glider's position does not change when the blocking device is removed, the transition from non-extended dwell to an extended dwell is referred to as positive action. The distance from the glider's connection to the platen to the rigid arm's connection to the crank is not altered by removing the blocking device. Therefore, the platens' position must be adjusted by the operator so that they will contact sooner.
Using the bushing spacers is cumbersome and inefficient because several steps are necessary to replace the spacers to provide the desired dwell duration. These steps typically involve removing a rod that extends from the glider through the end of the arm and provides a track for the bushing as the glider slides. The rod is held in place by screws and must be freed before removal, and once the rod is removed, the bushing can be removed as well. The desired bushing is inserted and the rod is replaced unless the bushing inserted placed the system in the rigid mode. Additionally, each time the duration of the dwell needs to be altered by changing the bushings, such as converting the system from a fully extended dwell to the rigid non-extended dwell, the platens' relative positions must be altered so that contact is established at the appropriate time in the crank's cycle.